Several engineering systems, including nuclear power plants, use safety valves to ensure a flow path is opened in the case of malfunction, emergency, or needed operational relief. Such flow paths may ensure fail-safe status or operation of important safety systems and include valves that reliably open the flow paths in desired circumstances. FIG. 1 is a cross-sectional schematic of a related-art explosive safety valve 10 in a closed configuration. As shown in FIG. 1, in a closed configuration, flow at an inlet 11 of valve 10 is blocked by a shear cap 40 between inlet 11 and outlet 12. Shear cap 40 is attached to a casing of valve 10 at inlet 11 by shearing sections 45 that may readily or reliably break under known and desirable forces. Shearing sections 45 may still possess sufficient tensile and shear strength to keep valve 10 closed during normal operating conditions; for example, shearing sections 45 may have strength to withstand a normal operating pressure differential between inlet 11 and outlet 12. Shear cap 40 may be further retained by a ring 41 or other keeping device passing through shear cap 40 to retain the same while allowing some movement or rotation.
As shown in FIG. 1, an explosive cap 20 is paired with a moveable tension bolt 30 in a casing of valve 10. Tension bolt 30 may be moveable and configured to be separated and driven under an explosive force of explosive cap 20 but not under spurious vibrations or impacts. Explosive cap 20 may be an assembly including several initiators or squibs that are activated through a circuit 25 or other connector. Tension bolt 30 is positioned to vertically drive down onto a moveable shearing piston 31. Explosive cap 20 is positioned to explosively drive apart tension bolt 30 into shearing piston 31, forcing shearing piston 31 downward with extreme force. When unactuated, shearing piston 31 may be upwardly maintained by low-force springs or other holders.
FIG. 2 is a cross-sectional schematic of explosive safety valve 10 in an opened configuration. As seen in FIG. 2, exploded cap 20′ has separated and driven tension bolt 30′ into shearing piston 31. In turn, shearing piston 31 has vertically sheared off shearing sections 45 (FIG. 1), resulting in shearing cap 40′ becoming disconnected from inlet 11. A pressure of fluid flowing from inlet 11 to now un-blocked outlet 12 pushed shearing cap ′40 away from inlet 11, and retaining ring 41 may cause shearing cap 40′ to rotate downward in such a situation. Shearing cap 40′ may contact a sensor 35 in a casing of valve 10, which may signal to operators or automated systems that valve 10 has successfully opened. In this way, actuation of explosive cap 20′, potentially by an electric safety signal from connector 25, has caused related art valve 10 to open and remain open. Co-owned “ESBWR Design Control Document, Tier 2,” Revision 10 of April, 2014, Chapter 5, describes helpful technological context and is incorporated by reference herein in its entirety.